Over the centuries there have been numerous efforts to reduce rolling of ships and boats. The efforts range from the simplicity of a submerged bucket rigged out-board of a small boat when not under way to elegant automatic gyroscopically controlled articulated underwater ship stabilizer fins. Although adaptable to larger or smaller vessels, the present invention is disclosed in the context of offshore commercial fishing vessels, and in particular, of trawlers having outrigger booms which extend outboard athwartship. The outrigger booms are used to rig the troll lines for fishing as the boat trolls forward.
The prior art has taken advantage of the presence of outriggers on trawlers to rig devices generally called "stabilizers" or "birds" which, in practice, function merely by means of frictional drag to damp rolling of the boat. One commercially available device of this sort is described in U.S. Pat. No. 2,561,539 to Seward. Seward discloses a pair of delta shaped metal plates with a weight at the forward apex or nose of each. A mast or pylon extends upwardly from the delta plate. The pylons of these stabilizer devices each are rigged to a line which extends downwardly from the outriggers on each side of the boat. As the boat rolls to starboard, the port stabilizer device is said to remain horizontal (reason not disclosed) and resists upward movement as the line rigged to it is pulled upwardly. The starboard stabilizer line slacks and that stabilizer device tips downwardly because the nose weight places the center of gravity forward of the suspension line attachment point. It descends freely. As the boat begins to roll oppositely, the roles of the stabilizers reverse and the starboard device resists upward movement as the port device descends freely. The resistance to upward movement dampens the tendency to roll. The devices of the Seward patent are said also to function as the boat moves forward at trolling or cruising speeds, but require a change in attachment of the suspension line for each different speed.
In practice, stabilizer devices of the sort described by Seward do not remain horizontal during upward rolling movement. The only tendency to remain horizontal is due to the balancing of the drag force due to the wing area by the nose weight. If a high upward force is encountered, the balance will be overcome and the device suddenly will tip into a nose-up, near vertical attitude which offers little resistance. The result is a sudden extinction of damping and the boat rolls suddenly. The effect is undesirable. While underway, the affected device or "bird" rapidly "flies" upwardly and may breach or jump out of the water. On occasion, the affected prior art device may crash into, or even come aboard the vessel. FIG. 5 illustrates this kind of prior art device.
U.S. Pat. No. 3,260,232 to Douglas discloses a pair of outrigger borne stabilizer devices which resemble a model airplane of the sort controlled by a pair of wires. The devices disclosed by Douglas have symmetrical airfoil wings, a body or fuselage, and aft have a tail empennage of a vertical fin and a horizontal fin. A nose-heavy attitude and upward water-flow force exerted on the after empennage of the device on the side toward which the boat rolls causes it to dive. The wing-like portions are to act hydrodynamically as the boat moves forward. A pair of suspension wires spaced fore and aft together with the tail empennage are to cause the device to alter attitude (angle of attack or angle of incidence) depending upon which way the boat rolls. While under way, the objective is to cause the device to tend to "fly" downwardly when the roll is upwards and to use the downward hydrodynamic "lift" to resist the roll. Under conditions of no relative water flow, as when adrift, the device offers only the drag resistance of its area to dampen rolling.
U.S. Pat. No. 3,505,968 to Gorman discloses a moveable asymmetric foil keel or centerboard which mechanically can be oriented with respect to a sail boat to resist heeling or to help lift the hull when running before the wind.
U.S. Pat. No. 2,589,312 to Wilcoxon shows a protector paravane or "kite" intended to be towed at a maximum distance aft of, and laterally outboard from the vessel and in a vertical or on edge attitude. A depth control wing is actuated by a pressure bellows to control depth. The center of gravity is said to be forward of the center of drag pressure. In essence, it is a depth controlled drag device intended to hold the end of the tow cable far from the vessel very much like a child's kite holds the kite end of the string away from the child.